1. The Field of the Invention
The present invention relates to chip carrier devices for temporarily securing semiconductor chips to testing circuitry. In particular, the present invention relates to chip carriers that use C-shaped clips for providing a force on a semiconductor chip in order to temporarily secure the semiconductor chip to electrical contact points on the chip carrier.
2. The Relevant Technology
Frequently, after a semiconductor chip such as an integrated circuit is manufactured, a testing process is conducted on the semiconductor chip by subjecting it to a preselected set of input conditions in order to measure its response and other parameters. The testing process typically involves connecting electrical contact elements of the semiconductor chip to corresponding electrical contact structures on a testing device. Moreover, the connection made with the external circuitry is temporary such that the semiconductor chip may be subsequently removed and shipped to the consumer or used in a manufactured product.
As devices integrated in semiconductor chips continue to become smaller and more tightly packed, it has become increasingly difficult to establish electrical contact between semiconductor chips and external circuitry in testing devices. This is primarily due to the fact that the electrical contact elements and the pitch between nearest adjacent electrical contact elements on the semiconductor chips have progressively become smaller. It has been difficult and expensive to design testing devices that have electrical contact structures that are sufficiently small to be compatible with the contact elements of conventional semiconductor chips.
Some of the difficulties associated with testing conventional semiconductor chips have been addressed by using devices known as chip carriers or interposers. A typical chip carrier includes a printed circuit board or another dielectric substrate having electrical traces leading from an array of first contact points on a bottom surface thereof to an array of second contact points on the top surface thereof. The second contact points are typically tightly spaced so as to correspond to the contact elements of the semiconductor chip. In contrast, the first contact points have a greater pitch, or are more widely spaced, in order to electrically engage the external circuitry contained in the testing device.
In practice, testing operations are typically conducted by first temporarily securing a semiconductor chip to the chip carrier. This generally requires aligning the semiconductor chip with the chip carrier such that the contact elements of the semiconductor chip are in contact with the corresponding contact points of the chip carrier. Because the connection should be temporary for testing purposes, the semiconductor chip is normally pressed onto the chip carrier without being soldered thereto. In the past, structures such as that seen in FIG. 1 have been used to temporarily secure the semiconductor chip to the chip carrier. One example of the structure illustrated in FIG. 1 is disclosed in U.S. Pat. No. 5,367,253 to Wood et al. Substrate 10 has a first surface 12 with an array of first contact points 14 and an opposite second surface 16 with an array of second contact points 18. A semiconductor chip 20 is disposed on second surface 16 such that electrical contact elements 22 of semiconductor chip 20 are connected with second contact points 18.
In order to temporarily secure semiconductor chip 20 onto substrate 10, bridge structures 24 have commonly been used. The bridge structure may include support members in contact with substrate 10 for stabilizing bridge structure 24. Support members 26 may be attached to substrate 10 by means of slots (not shown) in the side of substrate 10 or by gripping first surface 12 of substrate 10. Furthermore, the bridge structure may include a substantially planar plate 28 attached to the support members 26. A leaf spring 30 is attached to plate 28 and extends to semiconductor chip 20. As bridge structure 24 is positioned on substrate 10 and is placed in contact with semiconductor chip 20, the leaf spring 30 is compressed toward plate 28 and exerts a downward force 32 onto semiconductor chip 20, thereby holding it in place over substrate 10.
While bridge structure 24 often functions suitably well for its intended purpose, there are some instances in which another system for temporarily holding a semiconductor chip on a substrate could be desirable. For example, as seen in FIG. 1, bridge structure 24 ordinarily extends a considerable distance above semiconductor chip 20. Often, however, it is desirable to reduce the amount of space above the semiconductor chip that must be occupied by the clamping apparatus in order to temporarily secure the semiconductor chip to testing circuitry.
In view of the foregoing, there is a need in the art for an improved structure for temporarily securing a semiconductor chip to testing circuitry. In particular, it would be advantageous to provide a chip carrier for securing a semiconductor chip while greatly reducing the amount of space needed above the semiconductor chip.
The present invention relates to chip carriers that used C-shaped clips for generating a force on a semiconductor chip in order to temporarily secure the semiconductor chip to contact points on a chip carrier. The clips generally do not extend to the region directly over the semiconductor chip. Preferably, the clips are instead positioned to the sides of the semiconductor chip and are placed in contact with a cover member that extends over the semiconductor chip. The clips exert a downward force on the cover member, which in turn presses the semiconductor chip onto the chip carrier substrate. The clips conveniently allow the semiconductor chip to be secured to and later removed from the substrate in connection with a testing procedure.
In one embodiment of the invention, the chip carrier includes a dielectric substrate having at least a first layer, which includes a printed circuit board or another suitable structure, such as a polyimide layer. Preferably, the substrate further includes a second layer on the first layer. The first layer has an array of first contact points on a lower surface thereof. The first contact points may be solder balls of a ball grid array, pins of a pin grid array, land pads of a land grid array, or the like, depending on the nature of the testing device to be used with the chip carrier. The second layer has an array of second contact points on a surface thereof Alternatively, the substrate includes only the first layer, in which case the second contact points are arrayed over a surface of the first layer opposite the first contact points.
In either case, electrical traces connect the first contact points with the second contact points. Preferably, the first contact points are more widely spaced and have a greater pitch than the second contact points. This allows the electrical contact elements of semiconductor chip to effectively have an increased pitch when attached to the chip carrier, thereby facilitating the establishment of electrical connection with external circuitry of the testing device.
One method for using the chip carriers and the clips of the invention involves first positioning a semiconductor chip on the substrate such that contact elements of the semiconductor chip are connected with the second contact points of the substrate. A cover member is then disposed on the semiconductor chip opposite the contact elements thereof. The cover member may have a resilient layer at the interface with the semiconductor chip so as to provide a cushioning effect as the cover member presses down on the semiconductor chip.
The force by which the cover member presses down on the semiconductor chip is generated by one or more C-shaped clips compressively attached to the substrate. Preferably, the chip carrier utilizes at least two clips and most preferably four clips. The clips may have a first member in contact with the substrate and a second member separated from the first member and in contact with the cover member. In one embodiment of the invention, the first member of the clip is removably attached to the substrate by being fitted into a slot in the substrate. Furthermore, each chip preferably has an elbow segment integrally attached to both the first member and the second member.
When the semiconductor chip is received by the chip carrier, the clips are at least slightly deformed such that the distance of separation between the first member and the second member is increased beyond an equilibrium value. Such deformation of the clips produces a countervailing force tending to restore the clip to its predeformed state. Accordingly, the clips are preferably positioned so as to direct the countervailing force onto the cover member in order to press the cover member in the direction of the substrate. After the testing procedure has been conducted, the semiconductor chip may be removed from the chip carrier.
In view of the foregoing, it can be appreciated that the C-shaped clips and the chip carriers of the invention provide a system for easily and reliably securing a semiconductor chip to external circuitry. In addition, the use of the clips in combination with the cover member greatly reduces the amount of occupied space over the semiconductor in comparison to prior art devices. In particular, the clips preferably do not extend to the region directly over the semiconductor chips, but instead remain to the sides thereof.